Epoxides are important chemical commodities which are employed as starting materials for the preparation of antifreeze compositions, humectants, pharmaceutical preparations, cosmetic formulations, as monomers for the preparation of polymers, and the like.
Epoxides such as ethylene oxide and propylene oxide currently are prepared by a vapor phase catalytic method and by the two-step chlorohydrin route, respectively. The vapor phase process in industrial production of epoxides is confined to the preparation of ethylene oxide. Higher olefins are not amenable to a vapor phase catalytic process to provide economic production of the corresponding epoxide.
The older chlorohydrin route is the principal industrial process which supplies the largest quantities of propylene oxide for commerce. This process is suitable for conversion of ethylene and propylene to their corresponding epoxides, but higher olefins are not particularly adaptable to the chlorohydrin route.
Another process for preparation of epoxides is that involving organic peroxide or hydroperoxide oxidation of olefins. This process appears to have wider application insofar as olefin structure is concerned than do the first two methods described. Highly substituted ethylenes such as tetramethylethylene and trimethylethylene react smoothly and rapidly with a peroxy compound to give the corresponding epoxides. However, ethylenic compounds having much lower degrees of substitution about the carbon to carbon double bond (e.g., ethylene and propylene) react sluggishly with peroxy compounds and the rate of formation of the corresponding epoxides is very slow.
Each of the above described processes has inherent disadvantages. For example, vapor phase catalytic oxidation of ethylene to ethylene oxide requires large volume equipment and the handling of large quantities of potentially explosive mixtures of ethylene and oxygen. The chlorohydrin route to propylene oxide essentially involves a two-step process and in addition, chlorinated byproducts are produced. The process involving hydroperoxide oxidation of olefins is potentially hazardous if relatively large quantities of peroxy compound are to be handled.
Other prior art processes which are more pertinent for purposes of the present invention involve liquid phase olefin epoxidation with molecular oxygen. These prior art processes propose a variety of approaches to an improved balance of reaction variables such as specific oxidation catalysts or catalyst-solvent systems, the presence of polymerization inhibitors, the use of neutralizing agents such as metal hydroxides, the control of oxygen pressure, and the like. These prior art processes are disclosed in U.S. Patents which include U.S. Pat. Nos. 2,279,470; 2,366,724; 2,530,509; 2,650,927; 2,741,623; 2,780,634; 2,780,635; 2,837,424; 2,838,524; 2,879,276; 2,942,007; 2,974,161; 2,977,374; 2,985,668; 3,153,058; 3,210,380; 3,228,967; 3,228,968; 3,232,957; 3,238,229; 3,275,662; 3,281,433; 3,428,658; 3,674,813; 3,980,676; and references cited therein.
Among the more recent developments are liquid phase reactions in which olefins are converted to epoxides by a photooxidation mechanism. For example, Japanese Pat. No. 80/09,004 [C.A. 92, 164507 (1980)] describes the epoxidation of propylene with oxygen in a polar solvent in the presence of sulfur dioxide under irradiation with light of at least 2600 angstroms wavelength.
In J. Am. Chem. Soc., 98(14), 4193 (1976), N. Shimizu and P. D. Bartlett report the results of photooxidation of olefins sensitized by .alpha.-diketones and by benzophenone. Epoxides are produced, as well as allylic hydroperoxides and oxetanes.
There is continuing effort to develop improved and more efficient processes for the production of epoxides from olefins.
Accordingly, it is a main object of this invention to provide an improved liquid phase process for converting olefins to epoxides with molecular oxygen.
It is another object of this invention to provide a photochemical process for efficient epoxidation of olefins in liquid phase with molecular oxygen.
It is a further object of this invention to provide a liquid phase photochemical process for converting propylene to propylene oxide with molecular oxygen at a space time yield (STY) rate of at least 15 grams per liter hour.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.